The present invention relates to a horizontal deflection amplifying apparatus, which is used for an automatic main power supply such as that for a cathode ray tube, a color picture tube and a high definition television.
The horizontal deflection of a general cathode ray tube employs a horizontal deflection amplifying apparatus, which requires a power supply voltage of about 80V. This supply voltage is provided by a switching power supply circuit or a linear power supply circuit. Although the switching circuit is highly efficient, switching noise associated with the switching circuit deteriorates picture quality by adversely influencing the deflection current. Hence, the linear circuit is the more widely used.
Referring to FIG. 1, a conventional horizontal deflection amplifying apparatus for a linear power supply circuit is comprised of a power supply 10, a deflection coil driver 20, a capacitor controller 30, and an autotransformer 40. The power supply 10 supplies constant (DC) voltages to the deflection coil driver 20 and to the capacitor controller 30 so that the autotransformer 40 can provide the necessary drive voltage to drive a horizontal deflection coil (see FIG. 3). The autotransformer 40 generates the deflection voltage appropriate for the horizontal deflection coil (yoke coil) of a television set, by a tap manually selected during fabrication according to the screen size of the television. The power supply 10 is shown in FIG. 2 while the deflection coil driver 20, the capacitor controller 30 and the autotransformer 40 are shown in FIG. 3.
Referring to FIG. 2, the collector-to-emitter voltage (approximately 5 V ) of a transistor Q.sub.1 is predetermined to reduce the inherent power loss of the power supply 10 and a transistor Q.sub.2 is provided to shut down the power supply circuit by switching off transistor Q.sub.1 which prevents electrical damage to the horizontal deflection circuit. To accomplish this, a semiconductor-controlled rectifier (SCR) Q.sub.3 is connected to the base of transistor Q.sub.2. When the proper trigger is applied to the gate of SCR Q.sub.3, the base of transistor Q.sub.2 is effectively grounded through the SCR.
Two means are employed for protecting the horizontal deflection circuit. First, when excess current flows through a resistor R.sub.1, a transistor Q.sub.4 reaches saturation and the gate of SCR Q.sub.3 is triggered and operation of the power supply circuit is stopped. Second, when the pulsed collector voltage (V.sub.CP) of a transistor Q.sub.5, i.e., an insulation-gated bipolar transistor (IGBT), of the deflection coil driver 20 of FIG. 3 exceeds approximately 1,000 V, a trigger signal is created and supplied to the gate of SCR Q.sub.3 through a comparator 11, thereby stopping operation of the power supply circuit.
Referring to FIG. 3, in the deflection coil driver 20, the .+-.15 V applied from the power source 10 drives IGBT Q.sub.5 according to a horizontal deflection signal H.sub.def and a supply voltage drives the deflection coil via a plurality of capacitors C.sub.1 -C.sub.14 and the autotransformer 40. That is, if the supply voltage is continually applied to the capacitor controller 30 according to the switching operation of the driven IGBT, the appropriate voltage V.sub.CP is generated between the emitter and collector of IGBT. The capacitor controller 30 is comprised of a plurality of capacitors C.sub.1 -C.sub.14 and relay switches K.sub.1 -K.sub.12 for selecting the capacitors. The autotransformer 40 includes a plurality of taps corresponding to relay switches K.sub.13 -K.sub.22 which selects the appropriate (screen size) inductance and which generate the proper deflection voltage for a yoke coil 50 of the television set. The autotransformer 40 also includes a plurality of relay switches K.sub.19 -K.sub.22 which are used for the fine-tuning of the deflection voltage.
In the above horizontal deflection amplifying apparatus, the capacitors are selectively connected so that the desired deflection current is supplied to the yoke coil. During such connection, however, the state of the circuit changes, thereby creating current transients of excessive voltage levels. Accordingly, to prevent such current transients the power source should be turned off just before the capacitors are connected and turned back on immediately thereafter.